1. Field of the Invention
The present invention relates to a hydrodynamic bearing type rotary device which utilizes a hydrodynamic bearing. The present invention additionally relates to a recording and reproducing apparatus that is equipped with such a device.
2. Description of the Related Art
In recent years the amount of memory in recording apparatuses has increased, and their data transfer rates have also increased. Because of this, the bearings used by such recording apparatuses must increasingly provide high levels of precision when spinning, as well as reliability. To that end, hydrodynamic bearing type rotary devices well suited to high speed rotation are used in these recording apparatuses.
A hydrodynamic bearing type rotary device rotates without contact between the shaft and the sleeve by using oil or other lubricating fluids introduced into the space between the shaft and the sleeve, with a pumping force being created by hydrodynamic grooves during rotation. The hydrodynamic bearing type rotary device is suited to high-speed rotation, because there is no contact and therefore no mechanical friction.
Hereinafter is a description of an example of an existing hydrodynamic bearing type rotary device, using FIGS. 26 through 36. As shown in FIG. 26, conventional hydrodynamic bearing type rotary devices include a sleeve 21′, a shaft 22′, a flange 23′, a thrust plate 24′, a seal cap 25′, oil 26′, a hub 27′, a base 28′, a rotor magnet 29′, and a stator 30′. The shaft 22′ is integrated with the flange 23′ and is rotatably inserted into a bearing hole 21A′ in the sleeve 21′.
The flange 23′ is accommodated in a step 21C′ in the sleeve 21′. A radial hydrodynamic groove 21B′ is formed in at least one of the external peripheral surface of the shaft 22′ and the internal peripheral surface of the sleeve 21′. Thrust hydrodynamic grooves 23A′ and 23B′ are formed respectively on the surface of the flange 23′ opposite the sleeve 21′, and on the surface of the flange 23′ opposite the thrust plate 24′. The thrust plate 24′ is fixed to the sleeve 21′. Bearing portion clearances in the vicinity of at least the hydrodynamic grooves 21B′, 23A′, and 23B′ are filled with the lubricating oil 26′. The pouch-shaped bearing portion clearances formed by the sleeve 21′, the shaft 22′, and the thrust plate 24′ are also entirely filled with the lubricating oil 26′ as necessary. The seal cap 25′ has a fixed part 25A′ attached to the top end surface of the sleeve 21′, as well as a tapered part 25B′ and a ventilation hole 25C′. A communicating hole 21G′ is provided substantially parallel to the bearing hole 21A′, and is provided so as to communicate an oil collector of the seal cap 25′ (the groove end of the radial hydrodynamic groove 21B′ on the side opposite the thrust hydrodynamic grooves) with the external periphery of the flange 23′ (the groove end of the thrust hydrodynamic groove 23B′ on the side opposite the radial hydrodynamic groove). The communicating hole 21G′, the radial hydrodynamic groove 21B′, and the thrust hydrodynamic groove 23B′ constitute a circulating channel for the oil 26′. The numerical symbol 35′ denotes an air bubble included in the bearing interior.
The sleeve 21′ is fixed to the base 28′. The stator 30′ is fixed to the base 28′ so as to face the rotor magnet 29′. The rotor magnet 29′ generates suction force in the axial direction through flux leakage, and pushes the hub 27′ towards the thrust plate 24′ with a force of about 10 to 100 grams.
The hub 27′ is fixed to the shaft 22′, and the rotor magnet 29′, a recording disk 31′, a spacer 32′, a clamper 33′, and a screw 34′ are fixed to the hub.
The operation of the conventional hydrodynamic bearing type rotary device shown in FIG. 26 will now be described using FIGS. 26 through 28.
The groove patterns of the radial hydrodynamic groove 21B′ and the thrust hydrodynamic groove 23B′ are designed so that when the shaft 22′ rotates, the pump force of the radial hydrodynamic groove 21B′, having a herringbone pattern, and the pump force of the thrust hydrodynamic groove 23B′, having a herringbone pattern or a spiral pattern, combine to convey the oil 26′ in the clearance of the tapered part 25B′ of the seal cap 25′ through the bearing hole 21A′ towards the external peripheral surface of the flange 23′, in the direction of the black arrows as shown in the drawings. The oil 26′ flows into the communicating hole 21G′ via the thrust hydrodynamic groove 23B′ and is circulated back into the tapered part 25B′ in the seal cap 25′. The shaft 22′ can thereby be rotated without coming into contact with the sleeve 21′ or the thrust plate 24′. As a result, data can be recorded and reproduced the rotating recording disk 31′ by a magnetic head or an optical head (not shown).
In FIGS. 27 and 28, the radial hydrodynamic groove 21B′ has an asymmetrical herringbone pattern in which the top half shown in FIG. 28 (L′ in FIG. 28) is longer than the bottom half (S′ in FIG. 28). The thrust hydrodynamic groove 23B′ has a spiral groove pattern as shown in FIG. 28, and the rotation of the shaft 22′ draws out the oil 26′ from the radial bearings in the direction of the arrow shown in FIG. 27, causing the oil 26′ to flow and circulate towards the external peripheral surface of the flange 23′. Thus the thrust hydrodynamic groove 23B′ creates a force that draws the oil in the radial hydrodynamic groove 21B′, as shown in FIG. 28. The pressure distribution between the radial bearing portion and the thrust bearing portion as shown in FIG. 28 then forms low-pressure parts, indicated by Pt′(−) or Pr′(−). When such low-pressure parts are created, air bubbles 35′ trapped in the oil 26′ accumulate in low-pressure parts. Problems have arisen in regard to wear and burn of the bearing portion (the radial bearing portion and the thrust bearing portion), caused when the air bubbles 35′ in low-pressure parts expand due to the difference in pressure, causing oil film breakage to occur at the radial hydrodynamic groove 21B′ or the thrust hydrodynamic groove 23B′. Wear and burn of the bearing portion is a significant problem, as it leads to a complete failure of operation of the rotary apparatus or entire recording apparatus. The radial hydrodynamic groove 21B′ in FIG. 27 is shown with an asymmetrical pattern, but the same problem occurs with a symmetrical pattern, where the top half and bottom half shown in FIG. 27 are of equal lengths (where L′=S′ in FIG. 27).
FIGS. 29 and 30 show a second structure of a conventional hydrodynamic bearing type rotary device. The second conventional hydrodynamic bearing type rotary device includes a sleeve 121 configured integrally with a second sleeve 121D, a shaft 122, a cover plate 136, oil 26′, a base 28′, and a hub 27′, as shown in FIG. 29. The shaft 122 is rotatably inserted into a bearing hole 121A in the sleeve 121. A radial hydrodynamic groove 121B is formed in at least one of the external peripheral surface of the shaft 122 and the internal peripheral surface of the sleeve 121. A thrust hydrodynamic groove 121H is formed on at least one of the bottom surface of the hub 27′ and the top surface of the sleeve 121. The cover plate 136 is fixed to the sleeve 121, the second sleeve 121D, or a base 28′. Bearing portion clearances in the vicinity of at least the hydrodynamic grooves 121B and 121H are filled with oil 26′. The pouch-shaped bearing portion clearances formed by the sleeve 121, the shaft 122, and the cover plate 136 are also entirely filled with oil 26′ as necessary. A communicating hole 121G is provided so as to communicate both ends of the bearing portions composed of the radial hydrodynamic groove 121B and the thrust hydrodynamic groove 121H. The numerical symbol 35′ denotes an air bubble trapped inside the bearing portion.
The following is a description of the operation of the second conventional hydrodynamic bearing type rotary device shown in FIGS. 29 and 30.
When the shaft 122 rotates, the thrust hydrodynamic groove 121H creates pressure as shown with Pt′ in FIG. 30, lifting the shaft 122. The radial hydrodynamic groove 121B creates pressure as shown with Pr′, causing the shaft 122 to rotate without contact. The groove pattern of the radial hydrodynamic groove 121B approximates a herringbone pattern. The groove pattern of the thrust hydrodynamic groove 121H is a spiral pattern. The groove patterns of the radial hydrodynamic groove 121B and the thrust hydrodynamic groove 121H are designed so that when the shaft 122 rotates, the pump force of the radial hydrodynamic groove 121B and the pump force of the thrust hydrodynamic groove 121H combine to convey the oil 26′ in the direction of the black arrows shown in FIGS. 29 and 30. The oil 26′ is then repeatedly circulated while flowing into the communicating hole 121G sequentially through the thrust hydrodynamic groove 121H and the bearing hole 121A.
The radial hydrodynamic groove 121B has an asymmetrical herringbone pattern in which the top half (L′ in FIG. 30) is longer than the bottom half (S′ in FIG. 30) as shown in FIG. 30, and the thrust hydrodynamic groove 121H has a spiral pattern as shown in FIG. 30. Because of this, the rotations of the shaft 122 cause the thrust hydrodynamic groove 121H to draw the oil 26′ from the radial hydrodynamic groove 121B in the direction of the white arrow as shown in FIG. 29. The pressure distribution between the radial bearing portion and the thrust bearing portion then forms low-pressure parts, indicated by Pt′(−) or Pr′(−) in FIG. 30. When such low-pressure parts are created, the air bubbles 35′ trapped in the oil 26′ accumulate in those low-pressure parts.
Problems have arisen in regard to wear and burn of the bearing portion, caused when the air bubbles 35′ in low-pressure parts expand due to the difference in pressure, causing oil film breakage to occur at the radial hydrodynamic groove 121B or the thrust hydrodynamic groove 121H. Wear and burn of the bearing portion is a significant problem, as it leads to a complete failure of operation of the rotary apparatus or entire recording apparatus. The radial hydrodynamic groove 121B in FIG. 29 is shown with an asymmetrical pattern, but the same problem occurs with a symmetrical pattern, where the top half and bottom half shown in FIG. 30 are of equal lengths (where L′=S′ in FIG. 30).
FIGS. 31 and 32 show a third structure of a conventional hydrodynamic bearing type rotary device. The third conventional hydrodynamic bearing type rotary device includes a sleeve 221 configured integrally with a second sleeve 221D, a shaft 222, a cover plate 236, oil 26′, a base 28′, and a hub 27′, as shown in FIG. 31. The shaft 222 is integrated with the flange 223 and is rotatably inserted into a bearing hole 221A in the sleeve 221. Radial hydrodynamic grooves 221E and 221F are formed in at least one of the external peripheral surface of the shaft 222 and the internal peripheral surface of the sleeve 221. A main thrust hydrodynamic groove 221J is formed in at least one of the opposite surfaces of the hub 27′ and the second sleeve 221D.
A sub-thrust hydrodynamic groove 221H is formed in at least one of the flange 223 and the bottom of the sleeve 221. The cover plate 236 is fixed to the sleeve 221, the second sleeve 221D, or the base 28′. Bearing portion clearances in the vicinity of at least the hydrodynamic grooves 221E, 221F, and 221H are filled with the oil 26′. The pouch-shaped bearing portion clearances formed by the sleeve 221, the shaft 222, and the cover plate 236 are also entirely filled with oil 26′ as necessary. A communicating hole 221G is provided to communicate both ends of a bearing portion composed of the radial hydrodynamic grooves 221E and 221F, and the thrust hydrodynamic groove 221H. The numerical symbol 35′ denotes an air bubble trapped inside the bearing portion.
The operation of the third conventional hydrodynamic bearing type rotary device shown in FIG. 31 will now be described using FIGS. 31 and 32. When the shaft 222 rotates, the main thrust hydrodynamic groove 221J creates pressure, lifting the shaft 222. The sub-thrust hydrodynamic groove 221H creates pressure as shown by Pt′ in FIG. 32, conveying the oil 26′. The radial hydrodynamic grooves 221E and 221F create pressure as shown by Pr′, causing the shaft 222 to rotate without contact. The groove patterns of the radial hydrodynamic groove 221E and 221F approximate herringbone patterns. The groove pattern of the sub-thrust hydrodynamic groove 221H approximates a spiral pattern. The groove patterns of the radial hydrodynamic grooves 221E, 221F and the sub-thrust hydrodynamic groove 221H are designed so that when the shaft 222 rotates, the pump force of the radial hydrodynamic grooves 221E and 221F and the pump force of the sub-thrust hydrodynamic groove 221H combine to convey the oil 26′ in the direction of the black arrow shown in FIGS. 31 and 32. The oil 26′ is then repeatedly circulated while flowing into the communicating hole 221G sequentially through the sub-thrust hydrodynamic groove 221H and the bearing hole 221A.
However, the sub-thrust hydrodynamic groove 221H has a spiral groove pattern as shown in FIG. 32, and at least one of the radial hydrodynamic groove 221E and 221F has an asymmetrical herringbone pattern in which the bottom half shown in FIG. 32 (L′ in FIG. 32) is longer than the top half (S′ in FIG. 32). Because of this, the rotations of the shaft 222 cause the radial hydrodynamic groove 221F to draw the oil 26′ from the sub-thrust hydrodynamic groove 221H in the direction of the white arrow as shown in FIG. 31. The pressure distribution between the radial bearing portion and the sub-thrust bearing portion then forms low-pressure parts, indicated by Pt′(−) or Pr′(−) in FIG. 32. When such low-pressure parts are created, the air bubbles 35′ trapped in the oil 26′ accumulate in those low-pressure parts. Problems have arisen in regard to wear and burn of the bearing portion, caused when the air bubbles 35′ in low-pressure parts expand due to the difference in pressure, causing oil film breakage to occur at the radial hydrodynamic groove 221F or the sub-thrust hydrodynamic groove 221H. Wear and burn of the bearing portion is a significant problem, as it leads to a complete failure of operation of the rotary apparatus or entire recording apparatus.
FIGS. 33 and 34 show a fourth structure of a conventional hydrodynamic bearing type rotary device. The fourth conventional hydrodynamic bearing type rotary device includes a shaft 322, a flange 323, a sleeve 321, oil 26′, a top cover 336, a hub 327, and a base 28′. The disk 31′ and the rotor magnet 29′ are attached to the hub 327. A lid 338 is attached to the base 28′. The shaft 322 is integrated with the flange 323. The shaft 322 is inserted into the bearing hole 321A of the sleeve 321 in such a manner as to be rotatable in a relative manner. The flange 323 faces the bottom surface of the sleeve 321 and forms a bearing portion. A radial hydrodynamic groove 321B is formed in at least one of the external peripheral surface of the shaft 322 and the internal peripheral surface of the sleeve 321. A thrust hydrodynamic groove 323A is provided in at least one of the bottom surface of the sleeve 321 and the top surface of the flange 323. The top cover 336 forms a clearance with the sleeve 321 and is fixed to either the sleeve 321 or the hub 327. The shaft 322 is attached to the base 28′. The disk 31′ and the rotor magnet 29′ are attached to the hub 327. A stator (not shown) is fixed to the base 28′ at a position that faces the external peripheral surface of the rotor magnet 29′. The rotor magnet 29′ generates suction force in the axial direction, which is downward in the drawing, pushing the sleeve 321 toward the flange 323 with a force of about 10 to 50 grams. The bearing portion clearances formed by the sleeve 321, the shaft 322, the top cover 336, and a lower cover 337 are entirely filled with oil 26′ as necessary. A communicating hole 321G is provided to communicate both ends of a bearing portion composed of the radial hydrodynamic groove 321B and the thrust hydrodynamic groove 323A. The numerical symbol 35′ denotes an air bubble trapped inside the bearing portion.
The following is a description of the operation of the fourth conventional hydrodynamic bearing type rotary device shown in FIGS. 33 and 34. When the sleeve 321 rotates, the thrust hydrodynamic groove 323A creates pressure as shown by Pt′ in FIG. 34, lifting the sleeve 321. The radial hydrodynamic groove 321B creates pressure as shown by Pr′ in FIG. 34, causing the sleeve 321 to rotate without contact. The groove pattern of the radial hydrodynamic groove 321B approximates a herringbone pattern. The groove pattern of the thrust hydrodynamic groove 323A approximates a spiral pattern.
The groove patterns of the radial hydrodynamic groove 321B and the thrust hydrodynamic groove 323A are designed so that when the sleeve 321 rotates, the pump force of the radial hydrodynamic groove 321B and the pump force of the thrust hydrodynamic groove 323A combine to convey the oil 26′ in the direction of the black arrows shown in FIG. 34. The oil 26′ is then repeatedly circulated while flowing into the communicating hole 321G sequentially through the thrust hydrodynamic groove 323A and the bearing hole 321A.
However, the thrust hydrodynamic groove 323A has a spiral groove pattern as shown in FIG. 34, the radial hydrodynamic groove 321B has an asymmetrical herringbone pattern in which the bottom half shown in FIG. 34 (L′ in FIG. 34) is longer than the top half (S′ in FIG. 34). Because of this, the rotations of the sleeve 321 cause the radial hydrodynamic groove 321B to draw the oil 26′ from the thrust hydrodynamic groove 323A in the direction of the arrow as shown in FIG. 33. The pressure distribution between the radial bearing portion and the thrust bearing portion then forms low-pressure parts, indicated by Pt′(−) or Pr′(−) in FIG. 34. When such low-pressure parts are created, the air bubbles 35′ trapped in the oil 26′ accumulate in those low-pressure parts. Problems have arisen in regard to wear and burn of the bearing portion, caused when the air bubbles 35′ in low-pressure parts expand due to the difference in pressure, causing oil film breakage to occur at the radial hydrodynamic groove 321B or the thrust hydrodynamic groove 323A. Wear and burn of the bearing portion is a significant problem, as it leads to a complete failure of operation of the rotary apparatus or entire recording apparatus. The thrust hydrodynamic groove 323A in FIG. 33 is shown with a fishbone-shape pattern, but the same problem occurs with a spiral pattern.
FIGS. 35 and 36 show a fifth structure of a conventional hydrodynamic bearing type rotary device. The fifth conventional hydrodynamic bearing type rotary device includes a shaft 422, a flange 423, a sleeve 421, oil 26′, a top cover 436, a hub 427, and a base 28′. The shaft 422 is integrated with the flange 423. The shaft 422 is inserted into a bearing hole 421A of the sleeve 421 in such a manner as to be rotatable in a relative manner. The flange 423 faces the bottom surface of the sleeve 421 and forms a bearing portion. Radial hydrodynamic grooves 421B and 423C are formed in at least one of the external peripheral surface of the shaft 422 and the internal peripheral surface of the sleeve 421. A thrust hydrodynamic groove 423A is provided in at least one of the bottom surface of the sleeve 421 and the top surface of the flange 423. The top cover 436 forms a clearance with the sleeve 421 and is fixed to either the sleeve 421 or the hub 427. The shaft 422 is attached to the base 28′. A disk (not shown) and a rotor magnet (not shown) are attached to the hub 427. A stator (not shown) is fixed to the base 28′ at a position that faces the rotor magnet. The bearing portion clearances formed by the sleeve 421, the shaft 422, and the top cover 436 are entirely filled with oil 26′ as necessary. A communicating hole 421G is provided so as to communicate both ends of the bearing portions composed of the radial hydrodynamic groove 421B and the thrust hydrodynamic groove 423A. The numerical symbol 35′ denotes an air bubble trapped inside the bearing portion.
The following is a description of the operation of the fifth conventional hydrodynamic bearing type rotary device shown in FIGS. 35 and 36. When the sleeve 421 rotates, the thrust hydrodynamic groove 423A creates pressure as shown by Pt in FIG. 36, lifting the sleeve 421. The radial hydrodynamic grooves 421B and 421C create pressure as shown by Pr′, causing the sleeve 421 to rotate without contact. The groove pattern of the radial hydrodynamic groove 421B approximates a herringbone pattern. The groove pattern of the thrust hydrodynamic groove 423A approximates a spiral pattern.
The groove patterns of the radial hydrodynamic groove 421B and the thrust hydrodynamic groove 423A are designed so that when the sleeve 421 rotates, the pump force of the radial hydrodynamic groove 421B and the pump force of the thrust hydrodynamic groove 423A combine to convey the oil 26′ in the direction of the black arrows shown in FIG. 36. The oil 26′ is then repeatedly circulated while flowing into the communicating hole 421G sequentially through the thrust hydrodynamic groove 423A and the bearing hole 421A.
However, the thrust hydrodynamic groove 423A has a spiral groove pattern as shown in FIG. 36, the radial hydrodynamic groove 421B has an asymmetrical herringbone pattern in which the bottom half shown in FIG. 36 (L′ in FIG. 36) is longer than the top half (S′ in FIG. 36). Because of this, the rotations of the sleeve 421 cause the radial hydrodynamic groove 421B to draw the oil 26′ in the vicinity of the thrust hydrodynamic groove 423A or the radial hydrodynamic groove 421C in the direction of the white arrow as shown in FIG. 35. The pressure distribution between the radial bearing portion and the thrust bearing portion then forms low-pressure parts, indicated by Pt′(−) or Pr′(−) in FIG. 36. When such low-pressure parts are created, the air bubbles 35′ trapped in the oil 26′ accumulate in those low-pressure parts. Problems have arisen in regard to wear and burn of the bearing portion, caused when the air bubbles 35′ in low-pressure parts expand due to the difference in pressure, causing oil film breakage to occur at the radial hydrodynamic groove 421B. Wear and burn of the bearing portion is a significant problem, as it leads to a complete failure of operation of the rotary apparatus or entire recording apparatus.    [Patent Document 1] Japanese Laid-open Patent Application No. 8-331796    [Patent Document 2] Japanese Utility Model Application No. 2560501    [Patent Document 3] Japanese Laid-open Patent Application No. 2004-116623